Some observations on changes in ponds after application of Phoslock

Our farm is brackish water, salinity in the range 12 – 36 ppt.

Changes that we have observed after reducing PO₄ down to less than 0.05 mg/L, and holding Secchi in the 35 – 40 range include:

• we have observed that peak DO should not exceed about 30 - 40% above 100% saturation: if DO is going above 50% saturation and Secchi transparency is close to our optimum, then there is excess PO₄ to our requirements and PO₄ should be measured and Phoslock applied to remove the excess

• we have noticed a marked reduction in marine phytoflagellates and a tendency to "nano-chlorella" and diatoms : this is a major risk reduction as flagellates can cause toxicity eg P parvum,heterosigma, dinoflags.

• persistant arthrospira blooms can be managed by taking PO₄ down to 0.01 – 0.03 ppm.

• our electricity bills are down by about 20%: this is because nightime DO's are dropping more slowly and and not as far as previously. Also morning DO's are recovering very quickly.

• rotifers tend not to "bloom" to very high populations, but rather to be in a more steady population over a much longer time

• Ammonia is much less prone to build up to high levels...not sure why but maybe lack of N- fixing blue greens and/or more diverse plankton